In the 21st century, the source of energy and the environmental issue are two major challenges posed to the sustainable development of human beings. As solar energy has such features as inexpensiveness, cleanliness and regeneration, researchers from different countries are endeavoring to achieve its efficient and rapid utilization, conversion and storage. The semiconductor photocatalysis technique, which exhibits such features as high processing efficiency and absence of secondary pollution, can effectively degrade toxic and harmful pollutants, and thus has a wide prospect of being applied to solve environmental issues.
Zinc oxide (ZnO) is a semiconductor material having a band gap of 3.2 eV. Under irradiation of ultraviolet light, ZnO may be excited to produce photo-generated electron-hole pairs, and is thereby further subjected to oxidation-reduction reaction. As compared with the common TiO2 photocatalyst, ZnO has a higher electron transporting rate and a longer photon-generated carrier lifetime, such that it has a wide application prospect in such fields as photocatalytic degradation of organic pollutants and solar batteries. Furthermore, studies show that porous and hollow structures play an important role in improving the activity of photocatalytic materials. On one hand, these structures may offer more active sites; on the other hand, hollow structures also contribute to the repeated refraction and scattering of light, thereby improving the utilization rate of light.
In order to prepare hollow-structured ZnO particles, such templating agents as carbon spheres and silicon spheres are generally added during their preparation so as to obtain a hollow structure; thereafter, high-temperature calcination is conducted to remove these templates, thereby obtaining the hollow structure. However, the above method is relatively cumbersome, and ZnO hollow spheres can't be directly synthesized in one step. Moreover, high-temperature roasting may also result in cracking of hollow structures and agglomeration of particles.
No report has ever been made on the double-layer ZnO hollow sphere structure and synthesis method thereof.